TECHNIC. 497 



TECHNIC. 



In the treatment of the external and middle ear the usual 

 methods are employed. For the study of the epithelium in conjunction 

 with the adjacent bone the tissue is fixed and then decalcified, or sub- 

 jected to those fixing methods which accomplish both processes at the 

 same time. The latter method, however, can be applied only to very 

 small objects. 



The manipulation of the membranous labyrinth, especially that 

 of the adult, is a very difficult technical problem. Its isolation from the 

 petrous portion of the temporal bone without injury can be accomplished 

 only in well-advanced fetuses and in children, and even here a thorough 

 knowledge of the situation of the parts in the petrous portion of the tem- 

 poral bone is essential. Smaller animals, especially rodents, afford better 

 specimens. In the latter, the semicircular canals and cochlea give rise to 

 more or less distinct projections into the tympanic cavity. If the latter 

 be opened, the situation of the parts may be ascertained from without. In 

 the rabbit and guinea-pig, the entire cochlea projects into the tympanic 

 cavity, and may be easily removed in toto with a strong knife, and, as 

 the bony cochlea in these animals has very thin walls, it offers very little 

 resistance to the decalcifying fluid (use, for instance, 3% nitric acid). 



According to Ranvier's method (89), the cochlea is opened with 

 a scalpel in a 2 C / C solution of osmic acid in normal salt solution. After 

 twelve hours the cochlea is placed for decalcification in 2 % chromic acid, 

 which is frequently changed. In guinea-pigs, for instance, decalcification 

 is accomplished in a week. 



According to the method of Retzius (84), the opened cochlea is 

 treated for half an hour with a 0.5% aqueous solution of osmic acid, and 

 then for the same length of time with a 0.5% aqueous solution of gold 

 chlorid. The organ of Corti is then dissected out and examined as a 

 whole, or cut after carefully removing the bone. 



The labyrinth of the human adult is usually prepared as follows : 

 The apex of the petrous portion of the temporal bone is removed and the 

 upper semicircular canal, together with the cochlea, opened in Miiller's 

 fluid ; in this solution the pyramid is left for three weeks ; during the first 

 week the fluid is changed daily, and every two days during the following 

 weeks. The specimen is then washed for twenty-four hours in running 

 water, placed in 80% alcohol for two weeks, and finally in 96% alcohol 

 for two days. The preparation is now ready for decalcification. This is 

 done with 5% nitric acid, which is to be changed daily (ten days to two 

 weeks). Then follows washing for two days in running water, carrying 

 over into 80 % alcohol for twenty-four hours, then into 96% alcohol for 

 from six to eight days, and, finally, infiltration and imbedding in cel- 

 loidin (A. Scheibe). 



The following method may also be employed with good results : 

 The isolated pyramid with opened semicircular canal and cochlea is 

 treated with Miiller's fluid for two days at room-temperature, and then 

 for three weeks in a thermostat at 23 C. During the latter period, the 

 fluid should be changed. The specimen is then washed for forty -eight 

 hours in running water, treated for fourteen days with 80% alcohol, then 

 for eight days with 96% alcohol, decalcified, and further treated as in 

 the preceding method. 



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